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面试题 03.01. 三合一

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Symbols count in article: 2.3k Reading time ≈ 2 mins.

面试题 03.01. 三合一

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class TripleInOne {
public:
    TripleInOne(int stackSize) : stacks(new int[stackSize * 3 + 3]), top1(0), top2(stackSize + 1), top3((stackSize << 1) + 2), stackSize(stackSize) {
        
    }
    
    void push(int stackNum, int value) {
        switch(stackNum)
        {
            case 0 :
                if(top1 == stackSize)
                    return;
                stacks[++top1] = value;
                break;
            case 1:
                if(top2 == (stackSize << 1) + 1)
                    return;
                stacks[++top2] = value;
                break;
            case 2:
                if(top3 == stackSize * 3 + 2)
                    return;
                stacks[++top3] = value;
                break;
        }
    }
    
    int pop(int stackNum) {
        if(isEmpty(stackNum))
            return -1;
        switch(stackNum)
        {
            case 0 :
                return stacks[top1--];
            case 1:
                return stacks[top2--];
            case 2:
                return stacks[top3--];
        }      
        return -1;
    }
    
    int peek(int stackNum) {
        if(isEmpty(stackNum))
            return -1;
        switch(stackNum)
        {
            case 0 :
                return stacks[top1];
            case 1:
                return stacks[top2];
            case 2:
                return stacks[top3];
        }      
        return -1;        
    }
    
    bool isEmpty(int stackNum) {
        switch(stackNum)
        {
            case 0 :
                return top1 == 0;
            case 1:
                return top2 == stackSize + 1;
            case 2:
                return top3 == (stackSize << 1) + 2;
        }      
        return false;
    }
private:
    int* stacks;
    int stackSize;
    int top1;
    int top2;
    int top3;
};

/**
 * Your TripleInOne object will be instantiated and called as such:
 * TripleInOne* obj = new TripleInOne(stackSize);
 * obj->push(stackNum,value);
 * int param_2 = obj->pop(stackNum);
 * int param_3 = obj->peek(stackNum);
 * bool param_4 = obj->isEmpty(stackNum);
 */

review

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class TripleInOne {
public:
    TripleInOne(int stackSize) : sz(stackSize) {
        stack.resize(stackSize * 3);
        begin[0] = 0;
        begin[1] = sz;
        begin[2] = sz << 1;
    }
    
    void push(int stackNum, int value) {
        if(begin[stackNum] != sz * stackNum + sz)
            stack[begin[stackNum]++] = value;
    }
    
    int pop(int stackNum) {
        if(isEmpty(stackNum))
            return -1;
        return stack[--begin[stackNum]];
    }
    
    int peek(int stackNum) {
        if(isEmpty(stackNum))
            return -1;
        return stack[begin[stackNum] - 1];
    }
    
    bool isEmpty(int stackNum) {
        return begin[stackNum] == stackNum * sz;
    }
private:
    vector<int> stack;
    int sz;
    int begin[3];
};

/**
 * Your TripleInOne object will be instantiated and called as such:
 * TripleInOne* obj = new TripleInOne(stackSize);
 * obj->push(stackNum,value);
 * int param_2 = obj->pop(stackNum);
 * int param_3 = obj->peek(stackNum);
 * bool param_4 = obj->isEmpty(stackNum);
 */